High Energy Physics

The rich network of string dualities provides powerful constraints in the structure of the theory. The connection of ten-dimensional type II theories to eleven-dimensional supergravity compactified on a circle and on a torus allows one to compute many perturbative high genus terms as well as the complete sum of non-perturbative contributions to a given higher derivative coupling of the string effective action. The same duality connection leads to a series of surprising non-renormalization theorems. These control the UV behavior of maximal supergravity in lower dimensions, and indicate that N=8 supergravity in four dimensions might be a finite quantum gravity theory.

This talk presents some recent results in renormalizable noncommutative quantum field theory. After introducing the renormalization group approach in the commutative setting I will procede to its generalization to the simplest noncommutative model, $phi_4^{star 4}$ on the Moyal space. The well known phenomenon of ultraviolet/infrared mixing is cured by adding a harmonic potential term to the free action. Under the new renormalization group, adapted to the noncommutative geometry, this model turns out to be renormalizable to all orders in perturbation theory. Moreover it is {f asymptotically safe} at all orders in perturbation theory. The consequences of this results are discussed.

Explorations of the possibility that the quark masses, and more generally the particle mass spectra, could be dynamically generated in the context of massless QCD will be presented. The basic idea is that the large degeneracy of the free massless QCD could lead to a large quark condensate and its corresponding mass. Under the presence of this very massive quark, the other five ones could acquire smaller masses as argued by Fritzsch in his Democratic Symmetry Breaking scheme. Further, the lepton and neutrinos could get their masses through their interaction with quarks mediated by radiative corrections. In this case the stronger electromagnetic corrections could imply the larger lepton masses with respect to the neutrino ones, since these are only weakly interacting with the quarks.

Geometries produced by brane intersections preserving eight supercharges are constructed. Typical examples of such configurations are given by fundamental strings ending on D branes and by brane webs. Consistency conditions of supergravity are shown to impose certain requirements on the locations of the sources, and these restrictions are found to be in a perfect agreement with results of the probe analysis. This agreement serves as a nontrivial test of the duality between open and closed strings. Some applications to AdS/CFT correspondence are also discussed.